CD109 is a cell surface antigen that marks primitive progenitor and hematopoietic stem cells and activated platelets and T lymphocytes. To date, the function of CD109 in these cell types has remained largely unknown. While T cell CD109 has previously been implicated in the regulation of antibody inducing T helper cell function, but its role is poorly understood.
To date, no one has been able to isolate and sequence CD109 DNA or protein. There are many reasons for these problems including the very low levels of CD109 gene expression and the corresponding low level of protein expression and activity. Moreover the instability of CD109 in protein extracts, and its association with plasma membranes has contributed to the difficulties surrounding its isolation. Without the DNA and protein sequences, it is impossible to design rational strategies for the modulation of CD109 levels or activity, by modulating gene and protein expression. There is a need to identify these sequences in order to establish methods to modulate CD109 activity. Protein sequence information is important for the elucidation of protein structure and the ultimate design of chemical inhibitors that may modulate CD109 activity in vivo. There is also a need for cells which overexpress CD109 polypeptides or in which gene expression is reduced or blocked.